Video cameras and video systems have found widespread use in many entertainment, security, scientific and engineering applications. For many of these applications, continuous data acquisition at the highest possible frame rate is required. However, for some scientific and engineering applications where the target varies (or an attribute thereof) in time or position, it may be necessary to gate the acquisition of image data to coincide with an external event, e.g. a part passing on a conveyer belt or heating of a part induced by a laser. For these applications, intermittent data acquisition, or acquisition at a continuously variable rate may reduce data storage requirements yet provide a concise summary of the behavior of the target during a particular time interval.
Early video systems were based on visual analysis of images on a display screen, either in real time or during playback from a video tape or video disk. Subsequent improvements allowed analog video data to be digitized by frame grabber cards in a host personal computer. Today, cameras which output digital data directly are gaining popularity, particularly in infrared (IR) imaging. The use of a digital camera allows images to be processed numerically, by the host computer, without the errors due to digitization or loss of dynamic range common to analog frame grabbers. However, the computer memory available for image analysis and storage is finite, so that image sequences which can be routinely processed by a human observer, say, 30 seconds, may not be practical for a personal computer.
In these types of applications where the target phenomena to be imaged varies in time, it is useful to match the rate of data acquisition more closely to the rate at which the phenomena changes. For example, for nondestructive testing applications, where a target is imaged in the IR in order to monitor its surface temperature in response to a transient heating or cooling stimulus (e.g. a laser pulse or electrical current), it would be most desirable to capture data at the highest possible rate during and immediately after the heating event, since significant frame to frame variations are likely to occur during this phase. However, as the cooling rate of the target decreases, it may no longer be necessary to acquire data at the highest acquisition rate, since differences between adjacent frames are likely to be quite small as time passes. Ideally, a camera designed for this type of application would have a continuously variable frame rate. Unfortunately, such devices are considerably more expensive than fixed frame rate cameras. In the IR, the use of a variable frame rate camera to image a target which is either heating or cooling can pose significant technical problems, since the response of the individual detector elements on the camera focal plane array may need to be calibrated for specific integration times and temperature ranges, and the calibration tables may need to be changed in real time, as the frame rate and temperature vary.
In view of the above, an object of this invention is to provide both hardware and software which provides precise control over the timing of digital image data acquisition by a personal computer, and simulates the effect of a variable frame rate camera.
In view of the above, an object of this invention is to provide both hardware and software which simulates the effect of a variable frame rate camera.